Conducting polymers are increasingly being used in diverse fields. For example, in the field of electronic products, conducting polymers are typically used as antistatic films and conductive materials for organic transistors. With respect to commercialization, conducting polymers are extensively used as the solid electrolytic layer in solid electrolytic capacitors (SECs). These SECs are often used, in particular, in power circuits and CPU peripherals of personal computers, since SECs are smaller and have lower equivalent series resistance (ESR) at high frequencies.
One of the electrical characteristics of this SEC is withstand voltage, and this withstand voltage depends on the thickness of the dielectric film. In an aluminum SEC, for example, the dielectric film is formed by anodization, and thus the dielectric film becomes thicker in proportion to the anodization voltage. Accordingly, a higher anodization voltage results in a thicker dielectric film, and in turn a higher withstand voltage.
A basic structure of a conventional SEC as described above includes an anode made of a valve metal, the dielectric film formed on this valve metal and a solid electrolytic layer made of a conducting polymer formed on this dielectric film. In general, conducting polymer is used in unmodified form. Japanese Patent Laid-open Application No. 2003-158043 discloses an SEC with this structure.
In other cases, a conducting polymer is used with resin for the purpose of preventing any increase in leakage current resulting from mechanical stress sustained during assembly and thermal stress during packaging or mounting, and reducing shorting. This type of SEC is disclosed in Japanese Patent Laid-open Application No. H11-16783.
In the above conventional structure, however, it is also known that any leakage current in the SEC makes its solid electrolyte a high resistance material (HRM) due to the heat it generates. The HRM produced has a low withstand voltage, and thus the SEC becomes shorted in some cases. In particular, shorting is a serious problem in circuits running at high rated voltages.
In addition, the leakage current characteristic worsens if this conducting polymer is used as the solid electrolytic layer in an SEC.